1. Field of the Invention
The present invention relates to a detector for detecting a vector indicating the motion of an image (hereinafter referred to as an image-motion vector or a motion vector).
2. Description Related Art
A typical prior art of the detector has been proposed in the Official Gazette of JP-A-62-25590.
FIG. 1 is a block diagram showing this prior art. As shown, 1 denotes an input terminal for an image signal, 2 denotes a memory for storing representative points, which stores signals for pixels corresponding to the representative points in an input image signal, 3 denotes a difference-absolute value converter, which outputs absolute values of differences between the input signals, 4 denotes an accumulator, and 5 denotes a detecting circuit for a minimum point.
According to the prior art detector including the foregoing components, at first, continuous image signals of two fields or more are received at the input terminal 1. In the representative-point memory 2, two or more representative points are preset in a detecting region on a screen. The memory 2 stores a signal for a pixel positioned on each of the representative points in the input image signal. The difference-absolute value converter 3 operates to determine each difference between the value of a signal of a representative point of the previous field and that of a shifted point shifted by i horizontally and j vertically from a representative point of the current field and to derive an absolute value .vertline..DELTA.L.vertline. (i, j) of the difference, where i denotes a horizontal distance and j denotes a vertical distance. The accumulator 4 contains a table for the displacement (i, j) within a detecting area, in which table the signals sent from the difference-absolute value converter 3 are accumulatively added for each point of the displacement (i, j). The accumulator 4 sends out a resultant value as a correlative value .tau..vertline..DELTA.L.vertline. (i, j) for the displacement (i, j). The minimum-point detecting circuit 5 detects the displacement (i', j') which provides a minimum value in the correlative values and assumes it as a motion vector.
The aforementioned description has been directed to the representative-point matching system. Besides this system an, all-point matching system is also known. In place of storing only the signals of the pixels positioned at the representative points, this system stores signals of all the pixels on the detecting area. Then, like the foregoing system, it performs the steps of deriving an absolute value of a difference (i, j) between the previous field signal and a signal shifted by (i, j) from the current field signal, accumulatively adding the absolute values, and assuming, as a motion vector, a displacement (i', j') which provides a minimum value of these values.
The above-mentioned arrangement, however, derives only correlative values for a displacement within a defined area Hence, it has a shortcoming that no motion vector outside the defined area can be detected.
If a user quickly moves a video camera when he pans the camera or shakes his hands while holding the camera, for example, no motion vector can be detected.
For detecting a motion vector having such a large amplitude, it is necessary to derive correlative values within a very large area For example, as shown in FIG. 2, a large detecting area 7 is required for detecting a motion vector 6 having such a large amplitude. Thus, it gives rise to a shortcoming that the processing time becomes long and the circuit becomes complicated.
To overcome the above-mentioned shortcomings, it is, therefore, an object of the invention to provide an image-motion vector detector capable of detecting a motion vector within a detecting region broader than that of a conventional detector and also capable of greatly reducing the processing time and the scale of an electronic circuit involved.